The present invention relates to developer apparatus for electrostatographic printing machines and more particularly to a removable developer.
In an electrostatographic reproducing apparatus commonly in use today, a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image area contained within the usual document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas in the photoconductive insulating are to form a powder image on the photoconductive area. This image may subsequently be transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure. Following transfer of the toner image to a support surface, the photoconductive insulating member is cleaned of any residual toner that may remain thereon in preparation for the next imaging cycle.
In typical commercial applications of such apparatus, the developer material has a limited useful life. By developer material herein, it is intended to define the combination of toner and carrier as the developer. As the developer material is used, toner naturally has to be replenished in the mixture of carrier and toner to insure adequate supply of toner for the development process. In addition, the carrier itself has a limited life due to a variety of problems occurring with continued use. For example, the carrier may become impacted with toner thereby reducing or altering its triboelectric properties particularly with respect to the toner. In addition, it frequently happens that the individual carrier particles are coated with selected material to enhance the triboelectric properties and these coatings after prolonged use can deteriorate or indeed flake off. As the end of the useful life of the developer material approaches and then the quality of the copies being produced in the printing machine degrades. As the quality of copies produced degrades, the users become displeased resulting in the necessity of a service call by a trained technician to try to improve copy quality. In addition, when the developer material finally does fail, a service call by a trained technician is required to replace the developer material in the apparatus. Accordingly, it is desirable to be able to use developer material throughout the useful life of the electrostatographic machine.